Over the past ten years, there has been an explosive growth in the use of multi-channel neuronal recordings, for both basic neurobiology research as well as clinical applications (see, e.g., Chicurel, (2001) Nature, 412:266-8; Nicolelis et al., (1997) Neuron, 18: 529-37; and Nicolelis, (ed.), Methods for Neural Ensemble Recordings, CRC Press, Boca Raton, 1998). However, during this time, progress in these fields has been limited by the design of the electrodes and electrode arrays presently available for clinical and research applications. In particular, the relatively large size and low electrode density of the presently available electrode array designs has limited the density of implanted electrodes to about 32 channels (or electrodes) per square centimeter. In comparison, because of the extremely high-density of neurons in the human (and other mammalian) brain, many researchers and clinicians cite a density of about 100 more electrodes per square millimeter as a theoretically ideal density of implanted electrodes. Therefore any improvement in electrode density would greatly facilitate work in these fields.
Prior art brain research instrumentation includes movable single channel or single electrode mechanisms that are limited to recording from a single location in the brain. Early research tended to be concentrated in sensory portions of the brain such as the visual cortex. For example, the research would seek to identify what particular stimulus in the subject's visual field would cause an individual neuron in the visual cortex to fire. The prior art single electrode mechanisms were capable of being moved to different locations in the brain but were only capable of recording from a single neuron or a small neuron cluster at a time.
The prior art also includes apparatuses with multiple electrodes whose position in space is fixed relative to the other electrodes. These prior art electrodes are capable of recording timing or firing patterns of multiple neurons or multiple small clusters of neurons. The importance of being able to record timing patterns is helpful to understanding higher order functions of the brain. However, the multi-channel or multi-electrode prior art devices could only be employed in restrained subjects and were not capable of being moved within the brain.
Thus, neurology research and the development of clinical applications were limited by the number of electrodes and research was confined to only those patterns that occurred between the individual neurons or small neuron clusters that happen to be near the tips of the recording electrodes. Another disadvantage of the fixed array of electrodes is that the research is inherently limited to those brain functions performed by a non-moving subject.
Yet another limitation of prior art apparatuses is that they are unsuited to long-term implantation. In order to accurately study neural processes and to treat neural maladies, it is important to be able to acquire significant amounts of data over a long period of time. This is not possible using prior art apparatuses that cannot be implanted for long periods of time in the neural tissue of a subject.
Early efforts to implant electrodes in the brain tissue of a subject have met with some success, but still encounter many problems. In many prior art devices and methods, a wire, or wires, is implanted in the cortex, the wire is immobilized on the skull in some manner, and is connected to an amplification and recording device(s).
These prior art methods and devices are deficient because movement of the electrode within the skull can disrupt signal transmission or cause signal artifacts. Excessive rigidity of the electrode can cause, in addition to signal disruption, irritation and damage to the cortex. Additionally, there is the possibility of a local tissue reaction to the presence of a foreign body or scar tissue formation over time, which can decrease the usefulness of the electrode and the signal transmitted. Infection due to electrode wires can cause deleterious effects. Current implant electrodes have been used to record signals over a period of days or weeks, and in few instances, for several months. An electrode array is needed, therefore, that can transmit signals accurately over a longer period, since repeated operations on a subject to repair or replace an electrode are clearly undesirable. Additionally, freedom of movement is also often restricted by the bulky electrode arrays used by present techniques. Thus, it is desirable to have access to small electrode arrays that do not limit movement.
Further, it is desirable to simultaneously record data from large numbers of single neurons in comparatively small areas of a subject's brain. This can greatly enhance the quality and quantity of data recorded from a subject and can offer insight into neural processes and afflictions. However, to meet this desire, an apparatus preferably provides a high-density of implantable electrodes. By increasing the density of electrodes, a greater volume of data can be acquired, and thus a deeper understanding of neural processes can be obtained. Prior art apparatuses, however, are unsuited to this goal, due to their limited electrode density.
Yet another significant advantage in recording data from a large number of single neurons is that a wealth of basic neurophysiological data would become available, data that is not accessible through prior art electrode arrays. Questions regarding the functional organization of adjacent neurons, their relative activities during sensory perception, and their relative coordinated activities during motor output could be determined. Relative activity during conditioning and during learning of new tasks could be studied. Furthermore, implanting electrodes over different cortical areas could demonstrate functional interactions in a manner unavailable by any other means.
Summarily, prior art apparatuses do not disclose a high-density multichannel electrode array for long-term intra-cranial neuronal recordings. A high-density electrode array would be a great asset to researchers in the field of neurobiology and to researchers in related fields. The problem, then, is to develop a high-density multi-channel electrode array that can improve the density of implanted electrodes by a significant degree. The present invention solves this and other problems.